In a digital environment, watermarking involves insertion of a pattern of bits into data, such as a digital image, audio or video file. The term is derived by analogy to the watermarks imprinted on higher quality paper stationery. The pattern of bits may be used to protect the data's copyright, to identify a user to whom the data has been assigned or for other purposes.
Unlike watermarked paper stationary, wherein watermarks are intended to be somewhat visible, digital watermarks are intended to be completely invisible, or in an audio implementation, inaudible. Generally, the bits comprising the watermark must be sufficiently interspersed and mixed within the data to avoid identification and/or manipulation by unauthorized third parties. To provide utility, the digital watermark must be robust enough to withstand expected changes to the data, such as reductions from lossy compression algorithms.
Generally, watermarking schemes work by making data associated with the watermark appear as noise of a magnitude below a threshold of human recognition. To view a watermark, a program configured to extract the type of watermark message imprinted upon the data must be used.
While a watermark can be disguised as noise, cautious recipients of the data may attempt to process the data in order to find out the potential presence of a watermark. Where the watermark is poorly disguised, it may be identified, allowing those in possession of the data to act in accordance with that knowledge.
Accordingly, a need exists for better watermarking technology that is adapted to imprint data with watermarks designed to embed as many bits as possible together with implementation efficiency.